Multifamily Loan Assumption: Pricing the Supplemental Gap

Published October 22, 2026

A 2021-vintage agency loan at a low-3% coupon is the most valuable thing on many multifamily balance sheets right now, and a buyer can inherit it. The 10-year Treasury closed near 5.2% on September 25, 2026, per the Federal Reserve Bank of St. Louis (FRED) series DGS10, and a published rate sheet from Multi-Family USA for the week of September 1, 2026 showed conventional agency fixed executions quoted at roughly benchmark plus 110–170 basis points — figures the publisher describes as directional samples rather than quotes. Against that backdrop, a multifamily loan assumption can look close to free money. It usually is not, because the assumption does not close the equity gap on its own, and the piece that does — the supplemental — prices at today's market, not 2021's.

Figures in the worked example below are illustrative unless attributed, and individual loans vary.

What a multifamily loan assumption is actually worth at a 6.5% market rate

The value of a multifamily loan assumption is the present value of a coupon spread over the loan's remaining term, and nothing more. The sourced facts that frame it:

• The maturity pipeline is large. Roughly $875B of commercial and multifamily mortgage balances — about 17% of the $5.0T outstanding — were scheduled to mature during 2026, down about 9% from the $957B maturing in 2025, per the Mortgage Bankers Association (MBA) release of February 9, 2026. Assumable loans surface when those owners transact rather than refinance.
• Vintage coupons sit well below current pricing. The 10-year Treasury averaged roughly 1.4%–1.5% across 2021, per FRED series DGS10, against a close near 5.2% on September 25, 2026. Agency fixed-rate loans price as a spread over that benchmark, so 2021 vintages generally carry coupons several percentage points below today's executions — though the exact gap depends on each loan's spread and term.
• Supplementals are governed by tests, not appetite. Fannie Mae's supplemental mortgage loan term sheet lists availability 12 months after the senior loan closes, a required new appraisal, coverage as low as 1.30x and loan-to-value (LTV) up to 70% depending on asset class and use of proceeds, and a requirement that Fannie Mae be the sole debt holder on the property.
• Freddie Mac's window has a hard edge. Freddie Mac's Optigo supplemental product description requires 12 months of seasoning, a supplemental coterminous with the first loan, at least three years of remaining term on the first loan, a $1M minimum, and combined LTV up to 80% for a 7-year amortizing structure or 70% for full-term interest-only, with combined coverage minimums ranging from about 1.25x to 1.35x by term.

These terms are as published at the time of writing and are subject to change — the loan documents and the servicer govern.

Why the supplemental, not the assumed loan, sets the blended rate

What follows is a read of those terms rather than a forecast. An assumed loan is usually smaller than the buyer's target leverage, because it was sized against a 2021 valuation and has been amortizing since. The gap between the assumed balance and the proceeds the deal needs has to be filled by equity, by a supplemental, or by walking away from the leverage.

That makes the supplemental coupon the swing input. If the assumed piece is two-thirds of the stack, a spread of roughly 350–400 basis points between the assumed coupon and the supplemental shows up as only 120–135 basis points on the blended rate. If the assumed piece is a third of the stack, most of the benefit disappears. Underwriting the assumed coupon as the deal's cost of debt, rather than the proceeds-weighted blend, is a common way these models overstate coverage.

A worked example: one assumed first loan, one supplemental behind it

Example (illustrative). A 200-unit Class B property in a Sun Belt secondary market. Purchase price $26M. Trailing Net Operating Income (NOI) of $1.56M, a 6.0% cap rate on the price. In place is a 2021-vintage Freddie Mac Optigo 10-year fixed loan: $14.5M original balance at a 3.15% coupon, closed in March 2021 with two years of interest-only and then amortizing on a 30-year schedule, maturing March 2031 — roughly 4.5 years of remaining term, with a current balance of about $13.4M after 42 months of amortization. Annual debt service on the assumed piece runs near $748K now that the interest-only period has ended.

Sized against the published tests, combined LTV of 70% on $26M allows $18.2M of total debt, which leaves room for a supplemental of about $4.8M. At an illustrative 7.0% interest-only coupon, that adds roughly $336K of annual debt service. Combined Debt Service Coverage Ratio (DSCR) lands near 1.44x ($1.56M ÷ ~$1.084M) — above the 1.35x floor, so the LTV test binds first, not coverage. For comparison, a new 10-year agency first at an illustrative 6.50% — the September 25 benchmark plus a spread inside the published 110–170 basis point range — on a 30-year amortization and sized to a 1.25x coverage floor supports about $16.45M.

At these inputs the assumption stack carries about $1.75M more debt and still costs roughly $164K a year less, or about $820 per unit. On a five-year hold that is real money, and the coverage cushion is about 0.19x of DSCR wider. A new-loan rate at the low end of the quoted spread range would let the new first size larger and narrow the equity gap, and a supplemental priced above 7.0% would narrow the annual savings. How DSCR is calculated does not change; the debt service plugged into it does.

The line item people miss is the last row. Both pieces mature in March 2031. The assumption bought a cheaper coupon, not a longer runway — the entire capital stack refinances in about 4.5 years, at rates nobody can quote today, while the new-origination column has a decade. Every figure in the table other than the published agency tests is an assumption, and supplemental pricing in particular is only knowable from a live quote.

The terms that quietly resize the deal

• The supplemental window can already be closed. Freddie Mac's product description bars a supplemental during the final three years of the first loan and requires three-plus years of remaining term. A 2021-vintage loan written on a 7-year term matures in 2028 — assumable in 2026, but with no supplemental available. In the example above, losing the $4.8M supplemental moves required equity from about $7.8M to roughly $12.6M, or from 30% of the price to nearly half.
• The appraisal sizes the supplemental, not the contract. Fannie Mae requires a new appraisal for a supplemental. If value comes in below the purchase price, the combined LTV test sizes off that value, and the gap shows up as equity late in the process.
• The buyer is underwritten, not just the property. Servicer approval covers net worth, liquidity, and operating experience, and the transfer fee, legal costs, and servicing costs set by the loan documents and the servicer can be spent whether or not approval lands.
• No room behind the agency. Fannie Mae's term sheet requires it to be the sole debt holder, which can foreclose mezzanine or preferred-equity plans built to bridge the same gap.
• Prepayment cuts the hold short. Fixed-rate agency supplementals carry yield maintenance, so an early sale or refinance can give back part of the coupon savings. A below-market coupon is worth what the hold period can capture, as the multifamily refinancing crisis and agency lending under the 2026 caps both illustrate from the other direction.

These mechanics differ between the agencies — see Freddie Mac versus Fannie Mae — and are subject to change. Verify current terms directly with the lender or servicer.

Where this analysis breaks

The honest counter-case starts with price. Sellers and their brokers know what assumable debt is worth, and a good deal of that value is often already in the asking price. If the buyer pays a premium equal to the interest savings, the trade is a wash on economics while keeping every structural constraint — the short maturity, the sole-lender rule, the yield maintenance.

Second, the benefit is a spread, and spreads compress. A blended 4.2% is only advantageous while market pricing sits meaningfully above it. If agency coupons move lower over the hold, the savings narrow while the constraints remain in place.

Third, the maturity concentration is a genuine risk rather than a footnote. Both pieces coming due together in 2031 means one refinancing event for the whole stack. CBRE's H1 2026 Cap Rate Survey found wide disagreement among market participants about where multifamily yields head next, and described infill multifamily as among the more bearish segments in its sentiment read — which is a reason to treat the 2031 exit cap as a range rather than a number. The broader picture is covered in the CRE debt maturity wall.

Finally, the 7.0% supplemental coupon in the example is a placeholder. Supplementals are quoted case by case and can land well above or below it depending on term, structure, and property performance.

The takeaway

A multifamily loan assumption is worth underwriting at the blended rate, on the assumed loan's remaining term, with the supplemental sized against the published combined coverage and LTV tests — not at the seller's coupon over a fresh 10-year hold. The two questions that decide most of the outcome are answerable before an offer: how many years of term the first loan has left, and whether that leaves the supplemental window open at all.

Running the stack both ways — assumed plus supplemental against a clean new first loan, at the same price and the same NOI — tends to show that the assumption competes on annual cost and loses on runway. That trade may be worth making. It is worth making deliberately.

UWmatic is an AI-powered underwriting platform built for multifamily and mobile home park investors. Model an assumed first loan and a supplemental side by side, with the blended rate, combined DSCR, and the maturity date the whole stack shares. Try the free underwriting calculator →

This analysis reflects current market interpretations as of the publication date and may evolve as new data becomes available. Figures cited are drawn from public sources including Federal Reserve Bank of St. Louis (FRED) Treasury data, Mortgage Bankers Association maturity research, Fannie Mae and Freddie Mac multifamily product terms, the CBRE H1 2026 Cap Rate Survey, and a published lender rate sheet, and are subject to revision. Worked-example figures are illustrative. Nothing in this post is investment advice; readers should conduct their own diligence and consult qualified professionals before making investment decisions.